A group of UK students have engineered a new bacteria they call BacillaFilla. It swarms into concrete cracks, then secretes a gluey mixture that hardens into concrete filler. But what if this bacteria escaped into the wild and started reproducing?

Above, you can see three photos: On the far left is a concrete crack, and in the next two images (of increasing magnification) you can see the BacillaFilla at work filling in the crack. It's producing a mixture of calcium carbonate and a "bacterial glue" that combine with bacterial cells to fill in the crack snugly.

Students at Newcastle University in the UK created the BacillaFilla for the annual synthetic biology contest iGem, where all entries are required to have safety features. The BacillaFilla are designed with a "kill switch," which prevents them from reproducing outside the lab. They are also designed to extrude their concrete filler only when they are in contact with concrete.

BacillaFilla is the kind of biotechnology crossed with materials science that we'll see a lot of in the future. The researchers point out that patching concrete cracks with bacteria is far less environmentally harmful than whipping up a vat of cement. Naturally green, BacillaFilla is an industrial material of the future.

But what happens when that future arrives, and workers accidentally inhale some of that BacillaFilla? Maybe it lands on their teeth, whose calcium content is close enough to being like concrete that suddenly you've got workers with a mouthful of concrete. Or maybe you'll start to see walls and bridges growing tumors: Places where the BacillaFilla didn't stop growing after the cracks were filled in.